INTRODUCTION. XXXV11 



by the rupture of its perihola, before it can effect the 

 emission of its ecthorceum. At least I have never met with 

 an example of the contrary. 



It has long been known, that a very slight contact with 

 the tentacles of a polype is sufficient to produce, in any 

 minute animal so touched, torpor and speedy death. Since 

 the discovery of these cnidce, the fatal power has been 

 supposed to be lodged in them. Baker, a century ago, in 

 speaking of the Hydra, suggested that " there must be 

 something eminently poisonous in its grasp;" and this 

 suspicion received confirmation from the circumstance that 

 the Entomostraca, which are enveloped in a shelly covering, 

 frequently escape unhurt after having been seized. The 

 stinging power possessed by many Medusa, which is suf- 

 ficiently intense to be formidable even to man, has been 

 reasonably attributed to the same organs, which the micro- 

 scope shows to be accumulated by millions in their tissues. 



Though I cannot reduce this presumption to actual 

 certainty, I have made some experiments, which leave no 

 reasonable doubt on the subject. First — I have proved 

 that the ecthorceum when shot, has the power of penetrating, 

 and does actually penetrate, the tissues of even the higher 

 animals. Several years ago, I was examining one of the 

 purple acontia of Adamsia palliata : no pressure had been 

 used, but a considerable number of cnidce had been spon- 

 taneously dislodged. It happened, that I had just before 

 been looking at the sucker-foot of an Asterina, which 

 remained still attached to the glass of the aquatic box, by 

 means of its terminal disk. The cilia of the acontium had, 

 in their rowing action, brought it into contact with the 

 sucker, round which it then continued slowly to revolve. 

 The result I presently discerned to be, that a considerable 

 number of the cnidce had shot their ectkorcea into the 

 flesh of the sucking disk of the Echinoderm, and were seen 

 sticking all round its edge, the wires imbedded in its sub- 

 stance even up to the very capsules, like so many pins 

 stuck around a toilet pin-cushion. 



To test this power of penetration still farther, as well as 

 to try whether it is brought into exercise on the contact of 

 a foreign body with the living Anemone, I instituted the 

 following experiment. With a razor I took shavings of 

 the cuticle, from the callous part of my own foot, as from the 

 ball of the toe, and from the heel. One of these shavings I 



